This invention is related to the determination of trace metals dissolved in perfluorinated fluids.
Perfluoropolyalkylethers (PFPAE) are being developed by the U.S. Air Force as high temperature lubricants for the next generation of turbine engines. These fluids consist essentially of a mixture of fluorinated polyethers. For example, these fluids can be of the general formula R.sub.f O(Z).sub.m (Y).sub.n R.sub.f, wherein R.sub.f is a lower perfluoroalkyl group, such as CF.sub.3, C.sub.2 F.sub.5, C.sub.3 F.sub.7 and the like, wherein Z is --CX.sub.2 CX.sub.2 O--.--CX.sub.2 CX.sub.2 CX.sub.2 O-- or --CX.sub.2 OCX.sub.2 CX.sub.2 O--, wherein X is --F, --CF.sub.3, --C.sub.2 F.sub.5 and the like, and Y is --CFXO--, m and n are integers whose sum is between 2 and 200 and the ratio of n to ra is 0.1 to 10, and the Z and Y units are statistically distributed along the PFPAE chain. Commercial base fluids of this type have been available for some time, for example, Krytox.RTM. (DuPont), Fomblin.RTM. (Ausimont), Demnum.RTM. (Daikin) and the like.
While several PFPAE based lubricants are commercially available, there are no analytical methods for the analysis of metals, due to wear of bearing surfaces in these fluids. Analytical methods which are commonly used for conventional lubricants fall due to the insolubility of available metal standards in PFPAE fluids. Such methods include atomic absorption spectroscopy, emission spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and the like.
ICP-AES analysis is a technique for determining major, minor and trace elemental constituents of liquid samples. This technique is based upon generation of an inductively coupled plasma utilizing RF energy. Liquid samples are converted into an aerosol utilizing a nebulizer and injected into a plasma. As a sample enters the plasma, it undergoes desolvation, volatilization, atomization, excitation and finally emits photons characteristic of wavelengths of elements present in the sample. The intensity of the emission at characteristic wavelengths is used to determine the concentration of a element present in the sample while the wavelengths themselves determine what elements are present. The plasma is typically supported by argon gas, but other gases may also be employed. The most commonly used frequency for maintaining the plasma has been 27.12 Mhz, however, recently other frequencies including 40.68 Mhz have been employed.
Accordingly, it is an object of the present invention to provide metal standards for spectroscopic analysis which are both soluble and stable in PFPAE lubricants.
It is another object of the present invention to provide a method for the spectroscopic determination of wear metals in PFPAE lubricants.
Other objects and advantages of the present invention will be apparent to those skilled in the art.